The present invention relates to a three part type propeller shaft for a vehicle such as an automobile, and more particularly relates to such a three part type propeller shaft which incorporates four Hooke type universal joints, and which is notable for smoothness and lack of wobbling and vibration.
The present invention has been described in Japanese Utility Model Application Ser. No. Showa 61-011967 (1986), filed by an applicant the same as the applicant or the entity assigned or owed duty of assignment of the present patent application; and the present patent application hereby incorporates into itself by reference the text of said Japanese Patent Application and the claim and the drawings thereof; a copy is appended to the present application.
Further, the present inventors wish hereby to attract the attention of the examining authorities to copending Patent Applications Ser. Nos. 889,612, now U.S. Pat. No. 4,724,708, and 899,937, which may be considered to be material to the examination of the present patent application.
As a propeller shaft assembly for a vehicle such as an automobile, it has long been conventional to employ a single part propeller shaft coupled at its front end by a first Hooke joint to the power output shaft of the transmission and at its rear end by a second Hooke joint to the power input shaft of the differential device of the vehicle. Further, it is known to utilize a two part propeller shaft assembly made up from two propeller shaft elements coupled together by a second Hooke joint, and as before coupled at its front end by a first Hooke joint to the power output shaft of the transmission and at its rear end by a third Hooke joint to the power input shaft of the differential device of the vehicle; this type of two part propeller shaft assembly was introduced in order to reduce the vibration and consequent noise level during high speed operation.
There are also known in the art various types of automotive vehicle equipped with cross mounted engines, disposed in such a manner than the engine crank shaft extends transversely to the body of the vehicle, and such vehicles are normally of the front wheel drive type. However, recently there have been developed so called full time four wheel drive type vehicles, which are provided with a central differential apparatus for distributing power between the front wheels and the rear wheels of the vehicle. Such a central differential apparatus is typically provided with a selectably actuatable locking mechanism for selectably preventing it from providing differential action, at the will of the vehicle driver. Further, there are also known four wheel drive vehicles which can be selectably switched to two wheel drive operational mode or four wheel drive operational mode, i.e. so called part time four wheel drive vehicles. Both these types of vehicle may typically include a transversely mounted engine whose crank shaft and rotational power axis extends transversely to the longitudinal axis of the body of the vehicle. In four wheel drive type vehicles with such a transversely mounted engine arrangement, the distance between the output side of the engine and transmission unit and the front end of the differential device for the rear wheels becomes even greater than heretofore, and accordingly the propeller shaft assembly inevitably becomes longer. Accordingly, various types of three part propeller shaft assembly have begun to be utilized in such four wheel drive transverse engine type vehicle configurations. Such three part propeller shaft assemblies include three propeller shaft elements and four universal joints.
In more detail, such a three part propeller shaft assembly typically includes a first or front propeller shaft element rotationally coupled at its front end by a first universal joint to the rear end of the power output shaft of the engine, a second or center propeller shaft element rotationally coupled at its front end by a second universal joint to the rear end of said first propeller shaft element, and a third propeller shaft element rotationally coupled at its front end by a third universal joint to the rear end of said second propeller shaft element and rotationally coupled at its rear end by a fourth universal joint to the front end of the input shaft of the differential for the rear wheels of the vehicle. And the center propeller shaft element is typically rotatably and elastically mounted to the lower side of the floor of the vehicle body by two elastic center shaft bearing supports, one near each of its ends; this is done in order positively to support said center propeller shaft element and to limit the number of degrees of freedom of the propeller shaft assembly as a whole. With this kind of three part propeller shaft assembly, especially in the case in which it is fitted to a four wheel drive type automotive vehicle, in order to maximize the space within the passenger compartment of the vehicle and so as to minimize the irregularity in the floor of the vehicle caused by the provision of the propeller shaft assembly passing thereunder from the front of the vehicle to the rear, it is known and is in fact almost mandatory (due to the difference in the height of the transmissin or transaxle assembly and the rear wheel differential device, and due to the difference in the height of the vehicle body and the support portions for the center propeller shaft element which results from the need to maximize the space within the passenger compartment) for the three propeller shaft elements and the four joints to be extended, not in a straight line, but with each joint bent through its own characteristic angle, and typically with the center propeller shaft element held lower than the other two propeller shaft elements. Further, for reasons of cost and simplicity of construction, it is desirable to employ Hooke joints for as many as possible of these universal joints. Also, in order to absorb the rotational fluctuations created at the Hooke joints, it is typical to dispose adjacent Hooke joints in such a mannner as to have mutually opposite phases; an exemplary such prior art transmission system is shown in schematic skeleton form in FIG. 6 of the accompanying drawings and will be described hereinafter.
Further, two part propeller shaft assemblies which utilize three joints have been proposed which employ a Hooke joint for the first joint and which employ constant velocity type joints for the second and third joints; certain such propeller shaft assemblies are disclosed, for example, in Japanese Patent Laying Open Publication Ser. No. 59-38133 (1984), which it is not intended hereby to admit as prior art to the present patent application except to the extent in any case required by applicable law.
A problem that has occurred with such a system is as follows. In the above outlined construction, generally during the high speed operational condition the vibration level and the noise level are low, but upon occasion a new type of vibration noise phenomenon not seen in the case of vehicles provided with single part propeller shaft assemblies or vehicles provided with two part propeller shaft assemblies arises. This vibrational noise is considered to be caused by rotational fluctuations originating in the propeller shaft elements.
As is per se known, when a Hooke joint is bent through an angle and is transmitting load from one propeller shaft element to another, a secondary force coupled is created. Thus, wobbling and vibration are caused in the propeller shaft elements due to secondary force couples arising in the joint angles present between the three propeller shaft elements. In particular, when a full time four wheel drive vehicle including such a three part type propeller shaft assembly is operated with the central differential apparatus in the locked condition, or when a part time four wheel drive vehicle likewise incorporating such an assembly is operated in the four wheel drive condition, especially in the event that the engine is cross mounted and the engine, the transmission, the differential for the front wheels, and the front wheel drive shafts are integrally constructed and their various rotational axes are disposed substantially in parallel, then the engine and the rear wheel differential device will both tend to rotate somewhat upwards due to torque set up due to the rotational difference between the front wheels and the rear wheels of the vehicle; however, in the case of a straight mounted engine type vehicle, then the engine and the rotational axis of the front wheels are not parallel, and accordingly the rear wheel differential device will tend to rotate somewhat upward but the engine will not tend to rotate significantly upward. The angles of the various joints of the three part type propeller shaft assembly are thereby increased, and this causes increase in the secondary force couples described above, which causes the above explained problems of wobbling vibration and noise due to secondary force couples to be accentuated.
One possible countermeasure for coping with this problem of wobbling vibration and noise due to secondary force couples would be either to change the initial joint angles, i.e. to anticipate the upward rotation of the engine and of the rear differential device as described above and to determine the initial joint angles in the light thereof, or to set the spring constants of the two elastic center shaft bearing supports for the center propeller shaft element to be greater, i.e. to make said center shaft bearing supports stiffer by, for example, using a stiffer rubber element in their constructions. However, changing the initial joint angles in this way would lead to the problems of reduced space in the vehicle passenger compartment and of degradation of the noise characteristics in said passenger compartment; and, although the concept of increasing of the spring constants of the two elastic center shaft bearing supports is effective for preventing or reducing such wobbling vibration and consequent noise, the general noise level as well as the booming noise level within the passenger compartment are thereby undesirably increased, and also the durability of the center shaft bearing supports would be deteriorated, and accordingly these problems in practice make such solutions not practicable. As a result, substantial reduction by these methods of the wobbling vibration and consequent noise is not possible, in the light of the problems of passenger compartment noise and of center shaft bearing support durability.
The adoption of two part propeller shaft assemblies utilizing a Hooke joint for the first joint and utilizing constant velocity type joints for the second and third joints might also be conceived of, but this would invite a sharp cost increase, and accordingly is not acceptable from the point of view of economy of vehicle manufacture.